Syrian troops have resumed heavy shelling of the city of Homs, activists say, a day after the UN General Assembly called for an end to violence.
One opposition group said the bombardment was the heaviest since troops launched attacks on anti-government strongholds 13 days ago.
A senior Chinese envoy is meanwhile due to meet President Bashar al-Assad.
China and Russia voted against the UN resolution, which also called on Mr Assad to hand over power to his deputy.
The two countries also vetoed what would have been a legally binding UN Security Council resolution two weeks ago.
Parts of Homs have been battered by mortars and rockets fired by Syrian government troops for nearly two weeks, as they try to dislodge hundreds of rebels from the Free Syrian Army.
On Friday, shells were hitting the districts of Baba Amr, Inshaat, Bayada and Khaldiya, opposition and human rights activists said.
"The shelling is continuous. They are using rockets and mortars, which are falling on people's houses," Homs resident Abu Abdah told the BBC. "The damage is so huge, and the city has been isolated."
"We have no support. We have a lack of medical supplies and food. The Assad forces have prevented people leaving the city."
Hadi Abdullah of the Syrian Revolution General Commission told the AFP news agency: "It's unbelievable - extreme violence the like of which we have never seen before, with an average of four rockets every minute."
"There are thousands of people isolated in Homs. There are neighbourhoods that we know nothing about. I myself do not know if my parents are OK. I have had no news from them for 14 days," he added.
Government forces on the outskirts of Homs have yet to make a big push on the ground to wipe out all resistance, as they have promised to do.
The UK-based Syrian Observatory for Human Rights reported that nine unidentified bodies were found in Homs on Friday morning.
Later, security forces in several locations reportedly attacked demonstrators spilling onto the streets after Friday prayers, including in the suburbs of Damascus. The Observatory said one person died at a protest in the capital's western Mezzeh district.
The Local Co-ordination Committees, an activist group that organises and documents protests, reported that 45 people had been killed by security forces across the country, including seven in Homs and 12 army defectors who were executed in the southern province of Deraa.
The BBC's Jim Muir in neighbouring Lebanon says the passing of the resolution at the UN General Assembly clearly is not affecting events on the ground, but it gave all parties a chance to air their views.
One-hundred-thirty-seven member states voted for the motion, which called on the Syrian authorities "to stop all violence or reprisals immediately, in accordance with the League of Arab States initiative".
The regional grouping has called on Mr Assad to hand over power to his deputy, who would form a national unity government within two months.
"The UN General Assembly sent a clear message to the people of Syria - the world is with you," US permanent representative Susan Rice said.
Russia and China were amongst the 12 states who voted against the non-binding resolution. There were also 17 abstentions.
Before the vote, Russia's Deputy Foreign Minister Gennady Gatilov said the resolution was "unbalanced".
Syria's permanent representative, Bashar Jaafari, meanwhile argued that it was a message of support to the "extremists and terrorists" he said the authorities in Damascus were fighting, and warned that it would only lead to more violence.
But UN Secretary General Ban Ki-moon accused the Syrian authorities of committing "almost certain" crimes against humanity.
On Friday, Chinese Vice-Foreign Minister Zhai Jun, who has met some opposition figures, is due to meet President Assad in Damascus for talks.
Before leaving Beijing, he condemned violence against civilians and called on the Syrian government to respect the people's "legitimate" desire for reform.
But he added: "China does not approve of the use of force to interfere in Syria or the forceful pushing of a so-called regime change."
Our correspondent says the chances for successful mediation right now seem very slight.
Arab and Western powers will be meeting in Tunis in a week to step up support for the Syrian opposition. Two days after that, the government is going ahead with a referendum on a new constitution.
On Friday, France and the UK urged the Syrian opposition to unite and said it needed more international support to resist suppression.
"We cannot bring about a Syrian revolution... if the Syrian revolution does not make an effort to rally together and organise so that we can better help them,'' French President Nicolas Sarkozy told reporters after holding talks in Paris with UK Prime Minister David Cameron.
Mr Cameron meanwhile announced that the UK was sending food and medical supplies to help tens of thousands of people in Syria.